When a RADIUS (Remote Authentication Dial In-User Service) server receives user authentication information through, for example, a public network and an access server connected to the public network from a user terminal, it performs user Sax authentication processing and connection control, such as DNS (Domain Name System) server designation and PPP (Point-to-Point Protocol) connection designation, and acquires information which is necessary for accounting. If these processings are completed, for example, the user terminal is permitted to connect to the Internet and/or is able to receive special services. A RADIUS protocol is regulated in “RFC (Request For Comments) 2865” and “RFC2866”. The RADIUS Protocol uses UDP (User Datagram Protocol).
There exists a service which provides a network, which connects access servers installed at a plurality of access points, for example, for companies such as ISPs (Internet Service Providers). Companies which use this service can increase access means for their users, without making large changes to their own systems. Each company prepares the RADIUS server and connects it to the aforementioned network. To the network, a relay server is connected to distribute requests from users to RADIUS servers of companies which provide services for the users. This relay server records transfer results and grasps the amount of use precisely to do accurate accounting, and confirms and changes contents of packets.
In such an environment, if the RADIUS server of one company gets down by the fault and so on, an access server can not acquire a response for a request, so the access server resends packets for the same request repeatedly. Therefore, network traffic increases, and it causes the decline of response speed even toward RADIUS servers of other companies which are working normally. In addition, usually sent packets are managed by the access server, but a buffer overflow may occur in the access server due to the increase of traffic by resending the packet, and consequently, some packets may be lost and the relay server may be unable to do accounting accurately. The service provider has to examine log data of the relay server and/or the access server and to look for the packets sent at the fault, and then, it has to notify companies of the information concerning the packets. However, there are so many packets that the service provider often cannot perform these works. Thus, the increase of traffic at the fault has so many problems.